1. Technical Field
The present development pertains to chain tensioners used in chain drive systems.
2. Background Art
It is known in the prior art to drive auxiliary components of an engine system by a chain or belt driven off of a crankshaft or other driving sprocket. To accommodate slack in the chain due to momentary changes in torque requirements of the various components and changes in system tension due to stretching of the chain with aging, it is known to provide a chain tensioner to take up the slack. Consequently, a relatively constant tension in the chain is maintained regardless of operating condition and/or state of wear of the chain.
One type of chain tensioner cartridge 1 is shown in FIG. 1 which has a cartridge body 2 having a hollow cylinder within and a piston 3 which can move axially in the cylinder. Cartridge 1 is intended to be mounted proximate a belt drive system on an internal combustion engine or other energy conversion unit. To engage with such an energy conversion unit, external threads 4 are provided on the outer surface of cartridge 1 which engage with a threaded housing mounted on the energy conversion unit (not shown). Cartridge body 2 remains fixed with respect to the energy conversion unit. The length of chain tensioner 1 is determined by the position of piston 3 with respect to element 2. A spring 5 applies a force on piston 3. Additionally, hydraulic pressure acts on piston 3 when oil passage 6 is supplied a pressurized fluid supply, typically from an engine's lubricant supply. Oil passage 6 is coupled to a cavity 7 between cartridge body 2 and piston 3 via a check valve 8. The mechanical spring force and the hydraulic force are balanced against a chain 9 riding against piston 3. When there is slack, the forces push piston 3 upward which causes a bow in chain 9 riding on piston 3 and thus the slack is taken up. When there is an increased tension in chain 9 due to, for example, a rapidly changing engine speed, the force that chain 9 exerts on piston 3 causes piston 3 to retreat into cartridge body 2 to establish a new equilibrium of forces, i.e., the force of the chain balances spring and hydraulic forces. In FIG. 1, chain 9 rides directly on piston 3. This is one alternative. In many applications, piston 3 presses directly against a tensioning arm, which presses into the chain. Or, in other applications, a shoe is applied to piston 3 with the chain riding on the shoe.
Cartridge 2 mounts into a threaded housing on an energy conversion unit by engaging with threads 4. In some applications, finding space to package the mating thread set presents a challenge. Furthermore, with such a design, there must be space to rotate the cartridge 2 with respect to the energy conversion unit both during an initial build and during repair and replacement operations. There is a cost associated with machining threads on the outer surface of cartridge 2 and the mating internal threads on the power conversion unit. An alternative mounting system obviating the need for a threaded connection is desired.